Yet more template parameter inference refinement.

Cython/Compiler/PyrexTypes.py

@@ -2265,7 +2265,7 @@ class CArrayType(CPointerBaseType):
         if isinstance(actual, CArrayType):
             return self.base_type.deduce_template_params(actual.base_type)
         else:
-            return None
+            return {}
 
     def can_coerce_to_pyobject(self, env):
         return self.base_type.can_coerce_to_pyobject(env)
@@ -2403,7 +2403,7 @@ class CPtrType(CPointerBaseType):
         if isinstance(actual, CPtrType):
             return self.base_type.deduce_template_params(actual.base_type)
         else:
-            return None
+            return {}
 
     def invalid_value(self):
         return "1"
@@ -3516,7 +3516,7 @@ class CppClassType(CType):
         if self == actual:
             return {}
         elif actual.is_cpp_class:
-            self_template_type = self.template_type or self
+            self_template_type = self
             while getattr(self_template_type, 'template_type', None):
                 self_template_type = self_template_type.template_type
             def all_bases(cls):

tests/run/cpp_template_functions.pyx

@@ -15,6 +15,7 @@ cdef extern from "cpp_template_functions_helper.h":
         int overloaded(double x)
         T overloaded(pair[T, T])
         U overloaded[U](vector[U])
+        X overloaded[X](char* s, vector[X])
     cdef T nested_deduction[T](const T*)
     pair[T, U] pair_arg[T, U](pair[T, U] a)
     cdef T* pointer_param[T](T*)
@@ -114,5 +115,6 @@ def test_overload_GH1583():
     assert a.overloaded(p) == 2
     cdef vector[double] v = [0.25, 0.125]
     assert a.overloaded(v) == 0.25
+    assert a.overloaded("s", v) == 0.25
     # GH Issue #1584
     # assert a.overloaded[double](v) == 0.25

tests/run/cpp_template_functions_helper.h

@@ -39,6 +39,10 @@ class A {
         U overloaded(std::vector<U> v) {
             return v[0];
         }
+        template <typename U>
+        U overloaded(char* c, std::vector<U> v) {
+            return v[0];
+        }
 };
 
 template <typename T>